Ancient Supervolcano Created Giant Underwater Mountain Chain

The June 12, 1991 eruption column from Mount Pinatubo taken from the east side of Clark Air Base.

Credit: USGS

A supervolcano on the ocean floor might have spewed massive amounts
of lava in a rapid amount of time, new findings that could help reveal
the mysterious origin of some of these ancient goliaths, which may have
triggered mass extinctions through Earth's history.

Roughly a dozen supervolcanoes currently exist. Some are on land,
while others lie at the bottom of the ocean. Each has produced several
million cubic miles of lava — about three hundred times the volume of
all the Great Lakes combined — dwarfing the amount of lava produced by
the Hawaiian
volcanoes or the Icelandic
volcano that erupted recently.

The mystery lies in the origin of their magma, or molten rock within
the Earth. Magma rising from deep within the Earth has a different
isotopic and chemical composition than magma that forms just below
Earth's crust. Some ocean supervolcanoes, known as large oceanic
plateaus, show signs of a deep-mantle origin, while others possess
chemical signatures of magma from a much shallower depth.

To help solve this mystery, scientists went on an ocean expedition to
drill into a large, 145-million-year-old underwater supervolcano.
Located 930 miles (1,500 kilometers) east off the coast of Japan, the
Shatsky Rise volcanic mountain chain is one of the largest
supervolcanoes in the world, measuring roughly the size of California.
Its top lies about two miles (3.5 kilometers) below the sea's surface,
while its base plunges to nearly four miles (six kilometers) beneath the
surface.

Shatsky Rise formed at the intersection of three tectonic plates,
known as a triple junction, where the crust is thin, with magma coming
from near the surface. However, it also bears signs that it might have
originated from a "plume head" of magma rising from deep within the
Earth to the surface.

"Shatsky Rise is one of the best places in the world to study the
origin of supervolcanoes," said marine geologist and oceanographer
William Sager of Texas A&M University, who led the expedition with
co-chief scientist Takashi Sano of Japan's National Museum of Nature and
Science.

Layer in time

They found Shatsky Rise is made up of layers of hardened lava, with
individual lava flows up to 75 feet thick (23 meters). Preliminary
results from their expedition suggest the supervolcano might have
erupted over a period of a few million years or less — a rapid pace in
geologic time.

"If you have an eruption that melts a large area rapidly like that,
it would seem to me to favor of plume head theory that a blob of magma
from near the core-mantle boundary ewlled upward," Sager told LiveScience.

Critical to these results are magnetic stripe patterns in the
seafloor.

"What makes Shatsky Rise unique is that it's the only supervolcano to
have formed during a time when Earth's magnetic field reversed
frequently," Sager explained.

Evidence of these reversals in Earth's magnetic field, which happened
periodically over hundreds of thousands of years, were captured by
magnetically sensitive minerals in the lava, which preserved the way the
Earth's magnetic poles once pointed much like compasses.

"We can use these magnetic stripes to decipher the timing of the
eruption," Sager said. Initial shipboard lab studies showed that much of
the lava erupted rapidly.

These findings could shed light on ancient massive lava flows, such
as the Deccan Traps that erupted near the mass extinction that ended the
age of dinosaurs, or the Siberian Traps that occurred right near the
largest mass extinction in history at the Permian-Triassic boundary.

"These findings could shed light on the origins of supervolcanoes
whose timing seem to have curious links with mass extinctions," Sager
said.

Charles Q. Choi is a contributing writer for Live Science and Space.com. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica.